Cathode ray tube



3 9 K. SCHLESINGER 2,227,032

CATHODE RAY TUBE Filed March 50, 1938 Fig.2.

Fig.1! 7 21' Fig.3

Jnvenfop:

Patented Dec. 31, 1940 PATENT OFFHCE CATHODE RAY TUBE Kurt Schlesinger, Berlin, Germany, assignor, by

mesne assignments, to Loewe Radio, Inc a corporation of New York Application March 30, 1938, Serial No. 198,828

- In Germany April 4, 1932 3 Claims.

The present application is a continuation-inpart of my co-pending application Serial No. 663,593'filed-in the United States Patent Oflice on March 30, 1933. The said application Serial No. 663,593 is now abandoned.

The present invention relates to cathode ray tubes and more particularly to tubes having an indirectly heated equipotential cathode. The emissive spot of the cathode consists preferably of a recess in the end part of the minute cathode tube which recess is filled with emissive material.

It is well known that an emissive surface of the described kind does not furnish an emission of equal intensity on the whole surface and that the point of maximal emission intensity even varies with the integral intensity of the ray, thus depending on the anode voltage or on the ray controlling potential. Also the apparent form of the spot depends on the samevariables so that the focal distance and consequently the sharpness of the luminous point on the screen varies.

, as produced by the new cathode.

In Figs. 1 and 3, II is the cathode heated by the resistance l2 and provided with the emissive spot l4. I3 is a diaphragm acting as anode. The electrode according to the invention is a cylinder or ring l5 surrounding the cathode at its end very closely and overwhelming it only a little. In Fig. 1, the space between cathode and cylinder l5 has been exaggerated in order to show the virtual equipotential plane l6 when I5 is provided with a potential a little more negative than the cathode. The distribution of potentials is indicated by connection of the electrodes to a potentiometer 2|. By the eflect of the electrode l 5 the apparent surface of the cathode, from the point of view of the first anod l3 and the subsequent electron-optical device (not 11- lustrated), is as shown in Fig. 2.

In order to concentrate the electron my the cathode may further be surrounded in the usual way by a Wehnelt cylinder I1 as shown in Fig. 111. Such cylinder may, also as usual, control the intensity of the ray by connecting th cylinder to the potentiometer 2| through a resistance 23 and to the intensity control potential 24 through a condenser 22.

According to the invention it is also possible, as shown in Fig. 3, to give a constant negative potential to the Wehnelt cylinder I1 and to control the intensity of the ray for television purposes by means of the electrode l5. In this case I5 is biased negatively towards the cathode via a high resistance 23 and connected to the output 24 of the receiver via a condenser 22.

I claim:

1. In a cathode ray tube comprising an equipotential cathode having an electron-emissive spot, and a Wehnelt cylinder having a negative bias with respect to said cathode and connected to a ray controlling variable potential, an electrode consisting of an annular cylinder which is surrounded by said Wehnelt cylinder and itself closely surrounds the electron-emissive spot of said cathode and means to impart to said inner cylinder a slight negative potential with respect to said cathode.

2. In a cathode ray tube comprising an equipotential cathode having an electron-emissive spot, and a Wehnelt cylinder having a negative bias with respect to said cathode, an electrode consisting of an annular cylinder closely surrounding the electron-emissive spot of said cathode and means to impart to said cylinder a slight negative potential with respect to said cathode.

3. In a cathode ray tube comprising an equipotential cathode having at its end a recess filled with electron-emissive material to form an elec tron-emissive spot and a Wehnelt cylinder having a negative bias with respect to said cathode, an electrode consisting of an annular inner cyl inder which is surrounded by said Wehnelt cylinder and itself closely surrounds the electronemissive spot of said cathode, means to impart to said cylinder a slight negative bias with respect to said cathode and means to connect'one of said negative electrodes with a ray controlling variable potential.

KURT SCHLESlNGER. 

